The rho-like proteins (i.e., p21 proteins), like other GTPases, cycle between an active GTP-bound form and an inactive GDP-bound state (Nobes and Hall, 1994). Regulation of these forms was shown to be controlled by several proteins including guanine nucleotide exchange factors ("GEF") such as Db1 and GTPase activating proteins (Hart et al. 1991, Boguski and McCormicK, 1993). Members of the rho family of proteins, including RhoA, B, C, rac1, 2, CDC42Hs ("CDC42 Homo sapien"), and TC10, share at least 50% sequence identity with each other and 30% identity with other ras-like proteins (Nobes and Hall, 1994). Insight into the physiological function of rho and rac proteins emerged from recent reports described by Ridley and Hall (Ridley and Hall, 1992; Ridley et al., 1992), in which rapid cytoskeletal effects were detected when rho and rac proteins were micro injected into Swiss 3T3 fibroblasts. Activated rho induces stress fiber formation and focal contact (Ridley and Hall 1992) whereas activated rac induces the formation of membrane ruffles and lamelipodia (Ridley et al. 1992). Rho proteins are also implicated in other physiological roles associated with cytoskeletal rearrangements such as cell motility (Takaishi et al. 1993), cytokinesis (Kishi et al. 1993) and lymphocyte aggregation (Tominaga et al 1993).
Although the physiological function of CDC42 was shown to be essential in bud formation in yeast (Johnson and Pringle 1990), no similar physiological function was described for its mammalian homologue CDC42Hs. However, a hint for its role in mammalian cells came from a study demonstrating that the protooncogene Db1 exhibits GEF activity on rho and CDC42Hs (Hart et al. 1991). This observation suggests a role for rho-like proteins in cell transformation to a neoplastic state. However, not all proteins containing the Db1 domain demonstrate nucleotide exchange activity on rho-like proteins. For example, ray (Gulbins et al. 1993), Ect2 (Miki et al. 1993), ras GRF and bcr (Boguski and McCormick 1993) do not exert nucleotide exchange activity on rho, and the Db1 domain of bcr and ras GRF do not transform cells. A recent study suggests a direct link for rho and Db1 in vivo by demonstrating that vav and Db1 transformation is mediated by rho (Khosravi-Far et al. 1994).
p21 proteins are known to be integral components of signal transduction mechanisms leading to control of cell proliferation. Many pathological conditions result, at least in part, from aberrant control of cell proliferation or differentiation. For example, neoplasia is characterized by a clonally derived cell population which has a diminished capacity for responding to normal cell proliferation control signals. Oncogenic transformation of cells leads to a number of changes in cellular metabolism, physiology, and morphology. One characteristic alteration of oncogenically transformed cells is a loss of responsiveness to constraints on cell proliferation and differentiation normally imposed by the appropriate expression of cell growth regulatory genes.
Currently only a few effector molecules for rho-like proteins are known including rat brain kinase PAK65 (Manser et al. 1994) and p67-phox of NADPH oxidase (Diekmann et al 1994). From molecular function studies in phagocytes, it was demonstrated that rac 1 and 2 are involved in the control of superoxide generation by the NADPH oxidase (Abo et al. 1991, Knaus et al. 1991). Activated rac together with two other oxidase cytosolic components, p47-phox and p67-phox, assemble with the membrane bound cytochrome b.sub.558 to form an active oxidase (Segal and Abo 1993). The effector molecule for rac in this system is p67-phox (Diekmann et al. 1994). An additional molecular effector for rac and CDC42Hs was shown to be a rat brain serine/threonine kinase, which is activated by rac1 and CDC42Hs (Manser et al. 1994). Other studies suggested that CDC42Hs and rho also can activate PI3 kinase (Zhang et al. 1993; Zheng et al. 1994).
In view of the potential and varied roles for rho-like p21 proteins in physiological pathways and disease states, such as cell structural integrity, physiological roles associated with cytoskeletal rearrangements such as cell motility, cytokinesis, lymphocyte aggregation, tumor cell transformation and proliferation, metasteses, cell aggregation, and the paucity of understanding of the molecules and agents that selectively effect or modulate the activities of these proteins in one or more of these physiological pathways, there thus exists a need in the art for compounds and agents with effector and modulator activity and methods to identify these and related compositions and agents. Further, such agents can serve as commercial research reagents for control of cell proliferation, differentiation, and other p21-related conditions. Despite progress in developing a more defined model of the molecular mechanisms underlying the transformed phenotype and neoplasia, few significant therapeutic methods applicable to treating cancer beyond conventional chemotherapy have resulted. Such p21 protein modulating agents can provide novel chemotherapeutic agents for treatment of neoplasia, lymphoproliferative conditions, arthritis, inflammation, autoimmune diseases, apoptosis, and the like. These and other objects are provided by this invention.